Apparatus for variably adjusting the control times of gas exchange valves in an internal combustion engine

ABSTRACT

An apparatus for variably adjusting the control times of gas exchange valves in an internal combustion engine. The apparatus has a driving element, an output element, at least one pressure chamber, a pressurized medium supply device, and at least one pressure accumulator. The pressurized medium supply device allows pressurized medium to be fed to or discharged from the at least one pressure chamber. A phase angle of the output element relative to the driving element can be changed by supplying or discharging pressurized medium to or from the pressure chamber. The pressure accumulator encompasses a movable element that has a first pressure surface which partially delimits a storage space. The storage space is connected to the pressurized medium supply device. The movable element can be moved against the force of an energy store by pressurizing the storage space.

FIELD OF THE INVENTION

The invention relates to a device for variably adjusting the control times of gas exchange valves of an internal combustion engine, having a drive input element, a drive output element, at least one pressure chamber, a pressure medium supply device and at least one pressure accumulator, with it being possible for pressure medium to be supplied to or discharged from the at least one pressure chamber by means of the pressure medium supply device, with it being possible for a phase position of the drive output element relative to the drive input element to be varied by means of the supply of pressure medium to or discharge of pressure medium out of the pressure chamber, with the pressure accumulator having a movable element which is provided with a first pressure surface which partially delimits a store chamber, with the store chamber being connected to the pressure medium supply device, with it being possible by means of the pressurization of the store chamber for the movable element to be moved counter to the force of a force store.

BACKGROUND OF THE INVENTION

In modern internal combustion engines, use is made of devices for variably adjusting the control times of gas exchange valves in order to be able to make the phase relationship between the crankshaft and camshaft variable in a defined angle range between a maximum early position and a maximum late position. The device conventionally comprises an actuating device which is driven by a crankshaft and which transmits the torque of said crankshaft to the camshaft. Here, the actuating device has formed within it a hydraulic actuating drive which makes it possible to targetedly influence the phase position between the crankshaft and camshaft. A pressure medium supply device is provided for supplying pressure medium to the actuating device.

A device of said type is known for example from EP 1 025 343 B1. The device comprises two rotors which are rotatable relative to one another, with an outer rotor being drive-connected to the crankshaft and with the inner rotor being rotationally fixedly connected to the camshaft. The device comprises a plurality of cavities, with each of the cavities being divided by means of a vane into two oppositely-acting pressure chambers. By supplying pressure medium to and discharging pressure medium from the pressure chambers, the vanes are moved within the pressure chambers, thereby effecting a targeted rotation of the rotors relative to one another, and therefore of the camshaft relative to the crankshaft.

The pressure medium supply to the pressure chambers and the pressure medium discharge from the pressure chambers is controlled by means of a pressure medium supply device which comprises a pressure medium pump, a tank, a control valve and a plurality of pressure medium lines. Here, a pressure medium line connects the pressure medium pump to the control valve. In each case one further pressure medium line connects one of the working ports of the control valve to the pressure chambers. The pressure medium is conventionally extracted from the lubricant circuit of the internal combustion engine.

To ensure the function of the device, the pressure in the pressure medium system must exceed a certain value in all operating phases of the internal combustion engine. This is particularly critical in the idle running phases of the internal combustion engine, since the pressure medium pump is driven by the crankshaft and therefore the system pressure rises with the rotational speed of the internal combustion engine. The system pressure provided by the pressure medium pump is also dependent on the pressure medium temperature, with the system pressure falling with rising temperature. The pressure medium pump must therefore be designed so as to provide said system pressure which is sufficient under the most unfavorable conditions, in order to ensure a sufficiently fast adjustment of the phase position of the inner rotor relative to the outer rotor. To ensure the required adjusting speed even under the most unfavorable pressure conditions, such as for example high pressure medium temperatures and/or low rotational speeds, the pressure medium pump must be designed accordingly. As a result, use is made of pressure medium pumps which are designed for the peak demands of the actuating device, and which are therefore of excessively large dimensions during most operating phases of the internal combustion engine. It is alternatively possible to use controllable pressure medium pumps which provide pressure medium according to demand. In both cases, the increased expenditure has an adverse effect on the costs, the installation space requirement and the fuel consumption of the internal combustion engine.

U.S. Pat. No. 5,775,279 A discloses a further device of said type. In said embodiment, a pressure accumulator is arranged between the pressure medium pump and the control valve, which pressure accumulator communicates with the pressure medium supply device. Said pressure accumulator is filled with pressure medium in phases of high system pressure. When the system pressure falls, then the pressure accumulator is emptied automatically, as a result of which additional pressure medium is supplied to the pressure medium supply device. The phase adjustment of the device is assisted in this way.

A disadvantage of said embodiment is the fact that the pressure accumulator is emptied even if the system pressure falls not on account of an adjustment process but rather on account of other external circumstances, for example as a result of a drop in the rotational speed. Therefore, reduced pressure assistance and a smaller pressure medium volume from the pressure accumulator are available for a subsequent phase adjustment process.

A further disadvantage is that the maximum pressure with which the pressure accumulator can assist the pressure medium supply device corresponds to the pressure which prevailed in the pressure medium supply device directly before the phase adjustment process. When the engine controller transmits an adjustment demand to the device at high temperatures and low rotational speeds, then the pressure assistance from the pressure accumulator is less pronounced, because the system pressure with which the pressure accumulator was filled was low. This may have the result that the adjustment process cannot be carried out, or that the adjustment speed is considerably reduced. It is therefore necessary in this case, too, for the pressure medium pump to be designed for the peak load, with the resulting disadvantages.

OBJECT OF THE INVENTION

The invention is based on the object of providing a device for variably adjusting the control times of gas exchange valves of an internal combustion engine, with it being sought to ensure a functionally reliable adjustment of control times at high adjustment speeds in all operating phases of the internal combustion engine. Here, it should likewise be possible to dispense with an overdimensioning of the pressure medium pump (design for the expected peak loads), and with the use of variable pressure medium pumps.

The object is achieved according to the invention in that the movable element has at least one second pressure surface which partially delimits a control chamber, with it being possible by means of the pressurization of the control chamber for the movable element to be moved counter to the force of the force store, and with a pressure medium flow within the pressure accumulator from the store chamber into the control chamber being prevented.

Here, it may be provided that the store chamber and the control chamber do not communicate with one another within the pressure accumulator.

The movable element may for example be designed as a pressure piston which can be moved within a pressure reservoir counter to the force of a force store which is designed as a spring element. Alternatively, use may also be made of other types of force stores, for example reversibly deformable bodies, for example composed of elastomers, or gas-filled balloons. By forming the pressure accumulator with a movable element, which partially delimits chambers, which are isolated from one another within the pressure accumulator, said two chambers can be activated, that is to say filled and/or emptied, separately from one another. Aside from leakage, there is no connection between the chambers. It is thus possible, for example, to use different pressure sources for filling the store chamber and the control chamber.

It is alternatively also possible for a pressure medium connection to be provided within the pressure accumulator between the store chamber and the control chamber. Pressure medium which is supplied to the control chamber can pass via said pressure medium connection into the store chamber. Here, however, it should be ensured that a reversed pressure medium flow, from the store chamber into the control chamber, is prevented. This may be realized for example by means of a pressure medium duct in the pressure piston or in the housing of the pressure accumulator, in which pressure medium duct a check valve is arranged. In said case, the filling of the store chamber and of the control chamber may take place solely by means of the filling of the control chamber. When the pressure accumulator is to be emptied, then the control chamber is connected to the tank. The store chamber empties into the pressure medium supply device, and the control chamber empties, unpressurized, into the tank. A passage of pressure medium from the store chamber into the control chamber is prevented by the check valve.

If it is provided that a pressurization of the store chamber moves the movable element in the same direction as a pressurization of the control chamber, then the control chamber can assist the filling of the store chamber. For this purpose, the control chamber is likewise filled with pressure medium during the filling process of the store chamber. In this way, a force is exerted on both pressure surfaces of the pressure piston, as a result of which a higher force is stored in the force store (the spring element is compressed to a greater extent). When the filled pressure accumulator receives the command from the engine controller to assist the phase adjustment process, then the control chamber can be emptied independently of the store chamber. That is to say, while the store chamber is emptied into the pressure medium supply device and thereby assists the phase adjustment process, the control chamber can be ventilated to atmospheric pressure into a tank. With suitable design, the ventilation of the control chamber can take place more quickly than the emptying of the store chamber into the pressure medium supply device. The entire force which has been stored in the force store therefore acts on the store chamber via the first pressure surface. As a result, the pressure at the start of the assistance process can increase by a factor of

$\frac{A_{1} + A_{2}}{A_{1}}$

as a function of the load acting on the force store at said time. Here, A₁ corresponds to the surface area of the first pressure surface and A₂ corresponds to the surface area of the second pressure surface. If use is made, for example, of a spring element as a force store, then the pressure at the start of the assistance process is increased by the full factor

$\frac{A_{1} + A_{2}}{A_{1}}$

for as long as the spring has not yet reached its maximally compressed state.

The basis of the invention is that, in a device for variably adjusting the control times of gas exchange valves of an internal combustion engine, having a drive input element, a drive output element, at least one pressure chamber, a pressure medium supply device and at least one pressure accumulator, with it being possible for pressure medium to be supplied to or discharged from the at least one pressure chamber by means of the pressure medium supply device, with it being possible for a phase position of the drive output element relative to the drive input element to be varied by means of the supply of pressure medium to or discharge of pressure medium out of the pressure chamber, a movable element of the pressure accumulator delimits at least two chambers, which are formed independently of one another and which can be acted on with pressure, in the movement direction of the element. Here, at least one of the chambers (store chamber) is connected to the pressure medium supply device and, during a phase adjustment process, can be emptied into the pressure medium supply device. Furthermore, at least one further chamber (control chamber) is likewise acted on with pressure medium during the filling process of the store chamber and empties faster than the latter during the emptying process of the store chamber. This may take place for example to atmospheric pressure, into a tank. The control chamber therefore assists the filling process in that the movable element is deflected to a greater extent than would be the case without pressurization of the control chamber.

As a result of the increase of the pressure provided by the pressure accumulator, the pressure accumulator can accommodate peak consumptions, such that the pressure medium pump can be designed for the normal operation of the internal combustion engine. No overdimensioned or controlled pressure medium pumps are required in order to ensure a functionally reliable and fast adjustment of the phase position. The adjustment speed of the actuating device is additionally increased. Alternatively, for the same adjustment speed, the actuating device may be dimensioned to be smaller. The mass, mass moment of inertia and costs can be reduced in this way.

In one refinement of the invention, it may be provided that, during the operation of the internal combustion engine, the control chamber may be selectively connected to a pressure source or to a tank. The pressure source may for example be the pressure medium supply device or the pressure medium pump thereof, or a source separate from these, for example the pressure source of a servo consumer (for example the servo steering system). In the second case, it is possible for the pressure accumulator to be completely filled even in operating phases with low system pressure. The selective connection to a pressure source or to the tank is produced via control means, for example a 3/2 directional valve in the form of a switching valve (for example seat valve) or a proportional valve (for example slide valve). Consideration may alternatively be given to two control means, with one of the control means blocking or opening up the connection from the pressure source to the control chamber and with the other control means blocking or opening up the connection from the control chamber to the tank. The control means may for example be electromagnetically actuated hydraulic valves such as directional valves (for example switching or proportional valves), double check valves or the like. Said control means receive control signals from an engine control unit of the internal combustion engine, according to which control signals the pressure accumulator is filled or emptied. It is thereby possible to realize a wide variety of assistance strategies.

It is likewise conceivable to use hydraulically actuated control means. Here, it may be provided that the hydraulic actuating device of the control means communicates with the pressure medium supply device. The control means are thus automatically switched when the pressure in the pressure medium supply device falls below a defined value. This considerably reduces the regulating expenditure.

In one physical embodiment of the invention, it is provided that the control chamber can be emptied into a tank without diversion via a consumer. Here, the control chamber is preferably emptied to atmospheric pressure, conventionally via a proportional or switching valve.

In one refinement of the invention, control means are provided, with it being possible for the control chamber to be selectively connected to a tank or to the pressure source by the control means. The control means may for example be designed as a directional valve.

In an alternative refinement of the invention to this, it is provided that control means are provided, which, in a first state, block a pressure medium flow from the store chamber to the pressure medium supply device and permit a pressure medium flow to the store chamber and to the control chamber, and which, in a further state, permit the pressure medium flow from the store chamber to the pressure medium supply device and produce a connection between the control chamber and a tank without diversion via a consumer. Here, it may be provided that the store chamber and the control chamber are connected via a check valve, with the connection being arranged between the control means and the chambers, and with the check valve blocking a pressure medium flow from the store chamber to the control chamber.

The store chamber is thereby prevented from communicating with the pressure medium supply device in operating phases of the internal combustion engine in which no phase adjustment takes place but the system pressure nevertheless falls. The pressure medium volume and the pressure in the store chamber are therefore held at a high value.

Here, a store line which connects the pressure medium supply device to the store chamber and a control line which connects the control chamber to a pressure source may be provided.

Furthermore, the control means may be designed as a single directional valve which has in each case one port for the store line, the control line, the control chamber, the store chamber and the tank. This reduces the number of components and the regulating expenditure during the operation of the internal combustion engine.

Alternatively, the control means may comprise at least one first directional valve which is arranged in the control line. It may also be provided that the control means also comprise a second directional valve which is arranged in the store line. Here, the directional valves may be designed for example as switching valves or proportional valves. Alternatively, the control means may also comprise a double check valve which is arranged in the store line.

It is advantageously possible in the device according to the invention for a check valve to be provided between the control chamber and the pressure source, which check valve blocks a pressure medium flow from the control chamber in the direction of the pressure source. The pressure medium volume situated in the control chamber is therefore enclosed until said control chamber is connected to a tank. In this way, the movable element is held in the deflected position even if the system pressure falls, and thereby prevents an inadvertent emptying of the store chamber.

In one refinement of the invention, a check valve may be provided between the store chamber and the pressure medium supply device, which check valve blocks a pressure medium flow from the pressure medium supply device in the direction of the store chamber. In this way, pressure peaks generated in the actuating device are prevented from being transmitted into the pressure accumulator. The pressure medium flowing back from the pressure chamber of the actuating device during a pressure peak is therefore supported on the check valve, as a result of which the hydraulic rigidity of the device is increased, and therefore the adjustment speed is increased and the transmission of torque from the crankshaft to the camshaft is improved.

The pressure assistance of the pressure accumulator can thus be activated by simply switching one or more control means. Here, the pressure medium volume is provided which is collected in the store chamber in those operating phases of the internal combustion engine in which the phase position is held constant. Here, depending on the embodiment, the pressure provided by the pressure accumulator corresponds either to the present system pressure multiplied by a factor which may amount to up to 1+A₂/A₁, or corresponds to a maximum system pressure present during the filling phase multiplied by the same factor. The full factor 1+A₂/A₁ is present whenever the full storage capacity of the force store has not yet been exhausted, the spring element has not yet been compressed into a blocked state and/or the pressure piston still bears against the stops.

In one refinement of the invention, it is provided that the movable element has a third pressure surface which at least partially delimits a counterpressure chamber, with a pressurization of the counterpressure chamber moving the movable element in the opposite direction to a pressurization of the control chamber or of the store chamber. Therefore, the pressure which can be provided by the pressure accumulator is increased once again, since the force exerted by the force store on the movable element is now increased by the force generated by the pressure acting on the third pressure surface.

The pressure assistance of the pressure accumulator can be utilized during every phase adjustment process. For this purpose, the control means (directional valves and/or double check valves) are placed into the position in which the store chamber is emptied whenever a phase adjustment is demanded. In the operating phases between the phase adjustment demands, the pressure accumulator can be filled.

A further possibility is for the pressure assistance of the pressure accumulator to be activated according to demand. When the engine controller detects that the pressure or volume flow provided by the pressure medium pump is not sufficient for the phase adjustment, then said engine controller enables the pressure assistance by the pressure accumulator. This approach lengthens the times in which the pressure accumulator can be filled, and therefore the performance of the pressure accumulator during the pressure assistance.

It may alternatively be provided that the pressure assistance of the pressure accumulator be utilized merely as a “boost” function for critical adjustment processes which require for example a high volume flow or a high adjustment speed. When the engine controller detects that a critical adjustment process of said type should be initiated, then said engine controller enables the pressure assistance by means of suitable setting of the control means.

It is likewise conceivable for the control means to be formed in one piece with the control valve which controls the pressure medium flow to and from the pressure chambers of the actuating device.

In one physical embodiment of the invention, it is proposed that the ratio between the minimum throughflow cross section between the control chamber and the tank and the minimum throughflow cross section between the store chamber and the actuating device is greater than the ratio between the surface area of the second pressure surface and the surface area of the first pressure surface.

The maximum volume of the store chamber advantageously corresponds to at least two times the volume required for a phase adjustment from a maximum late position to a maximum early position.

The pressure accumulator may for example open out into the pressure medium line between the pressure medium pump and the control valve.

It may alternatively be provided that the pressure accumulator open out into one of the pressure medium lines which connects one of the working ports of the control valve to one group of pressure chambers. It is additionally possible in said embodiment for a second pressure accumulator to be provided which opens out into the pressure medium line which connects the other working port of the control valve to the other group of pressure chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention emerge from the following description and from the drawings, which illustrate exemplary embodiments of the invention in simplified form.

In the drawings:

FIG. 1 shows an internal combustion engine in only highly schematic form;

FIG. 2 a shows a longitudinal section through the actuating device;

FIG. 2 b shows a cross section through an actuating device;

FIG. 3 shows a first embodiment of a device according to invention; and

FIGS. 4-12 show further embodiments of a device according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of an internal combustion engine 1, indicating a piston 3, which is seated on a crankshaft 2, in a cylinder 4. In the illustrated embodiment, the crankshaft 2 is connected to an inlet camshaft 6 and an outlet camshaft 7 via in each case one traction mechanism drive 5, with it being possible for a relative rotation between the crankshaft 2 and the camshafts 6, 7 to be effected by means of a first and a second device 10. The devices 10 comprise in each case one hydraulic actuating device 10 a,b,c and a pressure medium supply device 37. Cams 8 of the camshafts 6, 7 actuate one or more inlet gas exchange valves 9 a or one or more outlet gas exchange valves 9 b, respectively. It is likewise possible for only one of the camshafts 6, 7 to be equipped with a device 10, or for only one camshaft 6, 7 to be provided, which is equipped with a device 10.

FIG. 3 shows a first embodiment of a device 10 according to the invention, having actuating devices 10 a,b,c of a pressure medium supply device 37 and a pressure accumulator 43. FIGS. 2 a and 2 b show an actuating device 10 a,b,c in longitudinal section or in cross section, respectively.

The actuating device 10 a,b,c has a drive input element designed as an outer rotor 22 and a drive output element designed as an inner rotor 23. The outer rotor 22 has a housing 22 a and two side covers 24, 25 which are arranged on the axial side surfaces of the housing 22 a. The inner rotor 23 is formed in the manner of an impeller and has a substantially cylindrical hub element 26, from the outer cylindrical lateral surface of which five vanes 27 extend in the radially outward direction in the illustrated embodiment. The vanes 27 are formed separately from the inner rotor 23 and are arranged in vane grooves 28 which are formed on the hub element 26. The vanes 27 are loaded in the radially outward direction with a force by means of vane springs 27 a which are arranged between the groove bases of the vane grooves 28 and the vanes 27.

Proceeding from an outer circumferential wall 29 of the housing 22 a, a plurality of projections 30 extend in the radially inward direction. In the illustrated embodiment, the projections 30 are formed in one piece with the circumferential wall 29. The outer rotor 22 is mounted on the inner rotor 23, so as to be rotatable relative thereto, by means of radially inner circumferential walls of the projections 30.

A sprocket 21 is arranged on an outer lateral surface of the circumferential wall 29, by means of which sprocket 21 torque is transmittable from the crankshaft 2 to the outer rotor 22 via a chain drive (not illustrated).

In each case one of the side covers 24, 25 is arranged on one of the axial side surfaces of the housing 22 a and rotationally fixedly connected to the latter. For this purpose, an axial opening is provided in each projection 30, through which axial opening extends a fastening element 32, for example a screw, which serves for rotationally fixedly fastening the side cover 24, 25 to the housing 22 a.

Within the actuating device 10 a,b,c, a cavity 33 is formed between in each case two projections 30 which are adjacent in the circumferential direction. Each of the cavities 33 is delimited in the circumferential direction by opposite, substantially radially extending delimiting walls 34 of adjacent projections 30, in the axial direction by the side covers 24, 25, in the radially inward direction by the hub element 26, and in the radially outward direction by the circumferential wall 29. A vane 27 projects into each of the cavities 33, with the vanes 27 being designed so as to bear both against the side covers 24, 25 and also against the circumferential wall 29. Each vane 27 thereby divides the respective cavity 33 into two oppositely acting pressure chambers 35, 36.

The inner rotor 23 is rotatable relative to the outer rotor 22 in a defined angle range. The angle range is limited in one rotational direction of the inner rotor 23 in that the vanes 27 come to bear against in each case one corresponding delimiting wall 34 (early stop 34 a) of the cavities 33. Similarly, the angle range is delimited in the other rotational direction in that the vanes 27 come to bear against the other delimiting walls 34, which serve as a late stop 34 b, of the cavities 33.

The phase position of the outer rotor 22 relative to the inner rotor 23 can be varied by pressurizing one group of pressure chambers 35, 36 and relieving the other group of pressure. The phase position of the two rotors 22, 23 relative to one another can be held constant by pressurizing both groups of pressure chambers 35, 36. Alternatively, it may be provided that none of the pressure chambers 35, 36 to be acted on with pressure medium during phases of constant phase position. As hydraulic pressure medium, use is conventionally made of the lubricating oil of the internal combustion engine 1.

To supply pressure medium to and discharge pressure medium from the pressure chambers 35, 36, a pressure medium supply device 37 is provided which is illustrated in FIG. 3. The pressure medium supply device 37 comprises a pressure source, which is designed as a pressure medium pump 38, a tank 39, a control valve 40 and a plurality of pressure medium lines 41. The control valve 40 has an inlet port P, a tank port T and two working ports A, B. In each case one of the pressure medium lines 41 connects the pressure medium pump 38 to the inlet port P, the first working port A to the first pressure chamber 35, the second working port B to the second pressure chamber 36, and the tank port T to the tank 39. Pressure medium can therefore pass from the pressure medium pump 38 to the inlet port P of the control valve 40 via the pressure medium line 41.

In a first position of the control valve 40, the inlet port P is connected to the first pressure chambers 35, while the second pressure chambers 36 are connected to the tank 39.

In a second position of the control valve 40, it is provided that none of the pressure chambers 35, 36 communicate with the tank 39 and the inlet port P.

In a third position of the control valve 40, the inlet port P is connected to the second pressure chambers 36, while the first pressure chambers 35 are connected to the tank 39.

During the operation of the internal combustion engine 1, an alternating torque acts on the camshaft 6, 7, which alternating torque is caused by the rolling of the cams 8 on cam followers. Here, the force of valve springs acts on the camshaft 6, 7 with a braking action until the gas exchange valve is fully open. The camshaft 6, 7 is subsequently accelerated by the force of the valve springs. Consequently, pressure peaks are generated within the actuating device 10 a,b,c, which pressure peaks cause the pressure chambers 35, 36 which are connected to the inlet port P to be emptied counter to the pressure medium pump 38, which leads to a considerable reduction in the adjustment speed. To prevent this, a check valve 42 a is provided in the pressure medium line 41 which connects the pressure medium pump 38 to the control valve 40. The check valve 42 a prevents the pressure medium from flowing back from the pressure chambers 35, 36 to the pressure medium pump 38 via the control valve 40. The pressure peaks are supported on the check valve 42 a, as a result of which an inadvertent emptying of the pressure chambers 35, 36 is effectively prevented and the rigidity of the torque transmission and the adjustment speed are increased.

The adjustment speed of the actuating devices 10 a,b,c is dependent on the provided pressure or the provided pressure medium volume flow of the pressure medium pump 38. The provided pressure, or the provided pressure medium volume flow, are in turn dependent on numerous factors, for example the rotational speed of the internal combustion engine 1 and the pressure medium temperature. To ensure the demanded adjustment speed even under the most unfavorable conditions, such as for example high pressure medium temperatures and/or low rotational speeds, the pressure medium pump 38 must be designed accordingly. As a result, use is made of pressure medium pumps 38 which are designed for the peak demands of the actuating device 10 a,b,c, and which are therefore of excessively large dimensions during most operating phases of the internal combustion engine 1. It is alternatively possible to use controllable pressure medium pumps 38 which provide pressure medium according to demand. In both cases, the increased expenditure has an adverse effect on the costs and the fuel consumption of the internal combustion engine 1.

To avoid said disadvantages, a pressure accumulator 43 is provided in the device 10 according to the invention. The pressure accumulator 43 comprises a movable element which is designed as a pressure piston 45 and which can be moved within a pressure reservoir 44 counter to the force of a force store. In the illustrated embodiment, the force store is designed as a spring element 46. However, other types of force store, such as, for example suitably shaped elastomer bodies or gas-filled balloons, are also conceivable.

The pressure piston 45 has two pressure surfaces 47, 48. Together with the pressure reservoir 44, the first pressure surface 47 delimits a store chamber 49 and the second pressure surface 48 delimits a control chamber 50. Here, the pressure piston 45 and the pressure reservoir 44 are designed such that no connection exists between the two chambers 49 and 50 within the pressure accumulator 43. In the illustrated embodiment, the movement path of the pressure piston 45 has been limited by stops 54 for this purpose.

The store chamber 49 is connected by means of a store line 51 to the pressure medium supply device 37, with the store line 51 opening out into said pressure medium supply device 37 downstream of the check valve 42 a.

The control chamber 50 may be selectively connected to a tank 39 or via a control line 52 to a pressure source or In the illustrated embodiment, the pressure medium supply device 37 serves as a pressure source. It is however likewise conceivable to use some other pressure source, for example the pressure medium pump 38 of a servo consumer, for example the servo steering system. In said case, the pressure medium flowing out of the control chamber 50 is conducted not into the tank 39 of the lubricating oil circuit of the internal combustion engine 1 but rather to the corresponding tank 39 of the servo consumer.

To control the pressure medium flow to and from the control chamber 50, a control means 60 in the form of a first directional valve 53 is provided. The first directional valve 53 has a pressure port P₁, a control chamber port A₁ and a discharge port T₁. The pressure port P₁ is connected to the pressure source, in the illustrated embodiment via the control line 52 to the pressure medium supply device 37. The control chamber port A₁ is connected to the control chamber 50 and the discharge port T₁ is connected to the tank 39. In a first control position of the first directional valve 53, the control chamber port A₁ is connected to the pressure port P₁, while the discharge port T₁ does not communicate with any of the other ports P₁, A₁.

In a second control position of the first directional valve 53, the control chamber port A₁ is connected to the discharge port T₁, while the pressure port P₁ does not communicate with any of the other ports T₁, A₁.

A further check valve 42 b may also be provided, which is arranged in the control line 52 and prevents a return flow of pressure medium from the control chamber 50 to the pressure medium supply device 37. When no adjustment demand is transmitted from the engine controller to the device 10 during the operation of the internal combustion engine 1, then the control valve 40 is situated in the second (central) position and the first directional valve 53 is situated in the first position. Consequently, no pressure medium flows to or from the actuating device 10 a. At the same time, pressure medium passes both via the store line 51 into the store chamber 49 and also via the control line 52 into the control chamber 50. The pressure medium introduced into the store chamber 49 or the control chamber 50 acts on the pressure surface 47 or the pressure surface 48, respectively, as a result of which the pressure piston 45 is moved in the direction of the stops 54 counter to the force of the spring element 46, such that the volume both of the control chamber 50 and also of the store chamber 49 increases.

When the pressure in the pressure medium supply device 37 falls, then the pressure in the store chamber 49 also falls to the same extent. On account of the pressure gradient between the control chamber 50 and the pressure medium supply device 37, the check valve 42 b in the control line 52 closes, as a result of which a pressure drop in the control chamber 50 and a discharge of pressure medium out of said control chamber 50 are prevented. As a result, the volume of the control chamber 50 and of the store chamber 49 remains constant despite the pressure drop in the pressure medium supply device 37. Here, the travel x by which the pressure piston 45 has been deflected out of its rest position is defined as follows:

$x = \frac{p_{\max}\left( {A_{1} + A_{2}} \right)}{D}$

where A₁ corresponds to the surface area of the first pressure surface 47, A₂ corresponds to the surface area of the second pressure surface 48, p_(max) corresponds to the maximum system pressure occurring during the filling phase, and D corresponds to the spring constant of the spring element 46. Here, the maximum movement travel is limited by the stops 54. The rest position is to be understood as the state of the pressure piston 45 in which the spring element 46 is relaxed to the maximum extent.

When a phase angle adjustment is demanded by the engine control unit, the control valve 40 is moved into its first or third position. Pressure medium therefore passes from the pressure medium pump 38 to the first or second pressure chambers 35, 36 respectively, as a result of which a phase adjustment is effected by the actuating device 10 a,b,c. When the volume flow fed by the pressure medium pump 38 is too low to ensure the adjustment, or when a higher adjustment speed is to be obtained, then the first directional valve 53 is moved into its second control position. In said control position, the control chamber 50 is connected to a tank 39. The pressure medium which is under pressure in the control chamber 50 is thereby connected to atmospheric pressure, as a result of which a rapid emptying of the control chamber 50 takes place. At the same time, the store chamber 49 is emptied into the pressure medium supply device 37. When the emptying of pressure medium out of the control chamber 50 takes place so quickly that the pressure piston 45 is supported solely by means of the first pressure surface 47 with respect to the store chamber 49, then the entire force of the spring element 46 acts only on the store chamber 49. The pressure p in the store chamber 49 at the start of the emptying process can therefore be defined as follows:

$p = \frac{p_{\max}\left( {A_{1} + A_{2}} \right)}{A_{1}}$

As long as the pressure piston 45 has not yet been fully deflected, that is to say does not bear against the stops 54.

Since the check valve 42 a is arranged in the pressure medium line 41 upstream of the store line 51, it is ensured that the entire pressure p and the entire volume of the store chamber 49 is available to the actuating device 10 a, and does not flow out into the oil gallery of the internal combustion engine 1. Therefore, not only is the present system pressure or the maximum filling pressure available, as is the case in applications with conventional pressure accumulators, but rather a pressure increased by the factor 1+A₂/A₁ is available. The pressure medium supply device 37 can therefore be provided with pressure assistance by setting the second control position in the first directional valve 53. It is thus possible for the adjustment speed of the actuating device 10 a to be significantly increased for the same dimensioning, or for the actuating device 10 a to be designed to be smaller for the same adjustment speed, without having to accept the disadvantages of an overdimensioned or a regulated pressure medium pump 38.

Embodiments are also conceivable in which the arrangement of a check valve 42 b in the control line 52 can be dispensed with. In operating phases of the internal combustion engine 1 in which the phase position is held constant, the pressure accumulator 43 is filled similarly to the embodiment described above. When the system pressure falls, then pressure medium is discharged out of both the store chamber 49 and the control chamber 50. This leads to a pressure drop in both chambers 49, 50, which leads to a movement of the pressure piston 45 in the direction of its rest position. In this embodiment, therefore, both the pressure medium volume which can be provided for the phase adjustment and also the providable pressure in the store chamber 49 are reduced. Nevertheless, the pressure increase in the store chamber 49 takes place when the first directional valve 53 is moved into the second switching position. In this case, the provided pressure p when the pressure piston 45 has not yet been fully deflected can be defined as follows:

$p = \frac{p_{sys}\left( {A_{1} + A_{2}} \right)}{A_{1}}$

where p_(sys) corresponds to the system pressure prevailing at the start of the pressure assistance. It is conceivable for this embodiment to be used in internal combustion engines 1 in which the required peak system pressure lies only slightly above the capacity of the pressure medium pump 38. In this case, it is possible to dispense with the check valve 42 b in the control line 52, as a result of which costs are reduced.

In order to implement the pressure increase, the ratio Q_(D)/Q_(V) of the pressure medium flow out of the control chamber 50 to the pressure medium flow out of the store chamber 49 must satisfy the following relationship:

$\frac{Q_{D}}{Q_{V}} > \frac{A_{2}}{A_{1}}$

To achieve this, it is provided that the minimum throughflow cross section A_(D) between the control chamber 50 and the tank 39 satisfies the following relationship:

$A_{D} > {\frac{A_{2}}{A_{1}}A_{V}}$

where A_(V) corresponds to the minimum throughflow cross section between the store chamber 49 and the actuating device 10 a, or the actuating device 10 a and the tank 39.

It is likewise conceivable for one or more further actuating devices 10 b, 10 c in addition to the first actuating device 10 a to be controllable by means of the pressure medium supply device 37 via further pressure medium lines 41 and further control valves 40. Here, the further actuating device 10 b can likewise profit from the pressure accumulator 43. For this purpose, the branch which leads to said actuating device 10 b is situated downstream of the check valve 42 a in the flow direction.

If the pressure accumulator 43 is to assist only the first actuating device 10 a, then the branch to the further actuating device 10 c should be arranged upstream of the check valve 42 a in the flow direction.

To ensure the functionality of the pressure accumulator 43, a vent 46 a of the spring chamber to the tank 39 is provided.

It is likewise conceivable for the check valve 42 a to be arranged downstream of the branch to the store line 51 (FIG. 4). In this case, the pressure peaks are supported between the actuating device 10 a,b and the branch to the store line 51. The pressure peaks therefore cannot reach the pressure accumulator 43, as a result of which more rigid torque transmission by the actuating device 10 a,b is obtained.

It is likewise conceivable for in each case one check valve 42 a to be used in the pressure medium line 41 upstream and downstream of the branch to the store line 51 (FIG. 5). Here, rigid torque transmission by means of the actuating device 10 a,b is achieved, and the pressure or the pressure medium volume of the store chamber 49 is also prevented from being discharged into the oil gallery of the internal combustion engine 1.

A further embodiment of the device 10 according to the invention is illustrated in FIG. 6. In this embodiment, in contrast to the embodiment illustrated in FIG. 3, an additional check valve 42 c is arranged in the store line 51. Said check valve 42 c prevents a flow of pressure medium from the pressure medium supply device 37 to the store chamber 49, as a result of which pressure peaks which are generated in the actuating devices 10 a,b,c cannot penetrate to the store chamber 49 of the pressure accumulator 43, but rather are supported on the check valve 42 c. The hydraulic rigidity of the device 10 is therefore increased, similarly to the embodiment from FIG. 5.

To fill the store chamber 49 of the pressure accumulator 43, a connecting line 55 is provided which opens out firstly into the control line 52 between the pressure medium supply device 37 and the first directional valve 53 and secondly into the store line 51 between the check valve 42 c and the store chamber 49. Here, an additional check valve 42 d may be arranged in the connecting line 55, which additional check valve 42 d prevents pressure medium from flowing from the store chamber 49 into the pressure medium supply device 37 between the pressure medium pump 38 and the check valve 42 a.

In a slight modification of the embodiment, the check valve 42 b and/or the entire pressure medium line 41 in which the check valve 42 a is arranged between the opening-out points of the pressure accumulator 43 could be omitted.

FIGS. 7 to 11 show further embodiments of a device 10 according to the invention. In said embodiments, control means 60 are provided both in the control line 52 and also in the store line 51, which control means 60 can block the passage of pressure medium at least in one direction.

In the embodiment illustrated in FIG. 7, a single control valve In the form of a directional valve 56 is provided. The directional valve 56 has a pressure port P₁, a control chamber port A₁, a store port V₁, a store chamber port B₁ and a discharge port T₁. The pressure port P₁ and the store port V₁ are connected to the pressure source, in the illustrated embodiment via the control line 52 or the store line 51, respectively, to the pressure medium supply device 37. The control chamber port A₁ is connected to the control chamber 50, the store chamber port B₁ is connected to the store chamber 49 and the discharge port T₁ is connected to the tank 39.

Furthermore, a connecting line 55 is provided which opens out firstly into the control line 52 between the directional valve 56 and the control chamber 50 and secondly into the store line 51 between the directional valve 56 and the store chamber 49. A check valve 42 d is arranged in the connecting line 55, which check valve 42 d prevents a pressure medium flow from the store line 51 to the control line 52.

In a first control position of the directional valve 56, only the control chamber port A₁ is connected to the pressure port P₁, while all the other ports B₁, T₁, V₁ are closed.

In a second control position of the directional valve 56, the store port V₁ communicates with the store chamber port B₁ and the control chamber port A₁ communicates with the tank port T₁, while the pressure port P₁ does not communicate with any of the other ports A₁, B₁, T₁, V₁.

When no adjustment demand is transmitted from the engine controller to the device 10 during the operation of the internal combustion engine 1, then the directional valve 56 is situated in the first control position. In this state, pressure medium can pass from the pressure medium supply device 37 into the control chamber 50 via the control line 52 and the directional valve 56. At the same time, the store chamber 49 is likewise filled via the connecting line 55. In this state, the pressure accumulator 43 behaves in a similar way to the pressure accumulator 43 illustrated in FIG. 3. The pressure piston 45 is moved counter to the force of the spring element 46, and the chambers 49, 50 are filled with pressure medium. When the pressure of the pressure medium supply device 37 falls, then the pressure in the control chamber 50 likewise falls. However, the store chamber 49 maintains the high pressure state since it is isolated with respect to the pressure medium supply device 37 firstly by the directional valve 56 and secondly by the check valve 42 d. The pressure accumulator 43 therefore maintains its filled state.

When the directional valve 56 is moved into the second control state, then firstly the control chamber 50 is emptied into the tank 39 and secondly the store chamber 49 is emptied into the pressure medium supply device 37. This process takes place similarly to the first embodiment (FIG. 3).

FIG. 8 shows a further embodiment according to the invention which differs from the preceding embodiment merely by the arrangement of the check valve 42 a. Here, the check valve 42 a is arranged similarly to the embodiment from FIG. 4. An embodiment similar to FIG. 5 with two check valves 42 a, in each case one upstream and downstream of the store line 51, is also conceivable.

FIGS. 9 to 11 show further devices 10 according to the invention which are substantially identical to those from FIGS. 7 and 8. In contrast to the latter, instead of a single control means 60 (with a single directional valve 56 in the illustrated embodiment), the devices 10 illustrated in FIGS. 9 to 11 are provided with two control means 60. Here, the first control means 60 controls the communication between the pressure medium supply device 37 and the store chamber 49, while the second control means 60 controls the communication between the pressure medium supply device 37, the control chamber 50 and the tank 39.

In the embodiment illustrated in FIG. 9, the first control means 60 is designed as a double check valve 42 e which, in a first control position, permits a pressure medium flow from the pressure medium supply device 37 to the store chamber 49 but prevents a pressure medium flow in the opposite direction. In the second control position, pressure medium flows are permitted in both directions.

In this case, the second control means 60 is the first directional valve 53 illustrated in the first embodiment.

In contrast to the embodiment according to FIG. 9, FIG. 10 shows an embodiment in which the double check valve 42 e is replaced with a second directional valve 57, in the specific embodiment a 2/2 directional valve. In a first control position, the second directional valve 57 does not permit any pressure medium flow between the pressure medium supply device 37 and the store chamber 49. In a second control position, the pressure medium can flow in both directions.

In contrast to the embodiment according to FIG. 10, FIG. 11 shows an embodiment in which the first directional valve 53 has been modified in such a way that, in the first control position, only a pressure medium flow from the pressure medium supply device 37 in the direction of the control chamber 50 is permitted, whereas a pressure medium flow in the opposite direction in the first directional valve 53 is prevented.

FIG. 12 shows a further aspect of the invention which is explained on the basis of the embodiment illustrated in FIG. 6. It is expressly pointed out that this aspect may be used in all the preceding embodiments. The device 10 differs from the device 10 shown in FIG. 6 in that the connecting line 55 between the first directional valve 53 and the control chamber 50 opens out into the control line 52, and that no vent 46 a of the spring chamber is provided. The spring chamber is in fact provided as a counterpressure chamber 58 which can be filled with pressure medium.

In this embodiment, the first directional valve 53 is provided with an additional counterpressure port G which communicates with the counterpressure chamber 58.

In a first control position of the first directional valve 53, the control chamber port A₁ is connected to the pressure port P₁, while the counterpressure port G communicates with the discharge port T₁.

In a second control position of the first directional valve 53, the control chamber port A₁ is connected to the discharge port T₁, while the pressure port P₁ communicates with the counterpressure port G.

When the first directional valve 53 is situated in the first control position, there are no changes in relation to the embodiment from FIG. 6. In the second control position, however, pressure medium is additionally conducted into the counterpressure chamber 58. This loads a third pressure surface 59 of the pressure piston 45 with a force which acts in the same direction as the spring element 46. The pressure in the store chamber 49 is additionally increased in this way.

In all of the illustrated embodiments, the pressure accumulator 43 opens out with the pressure medium line 41 which connects the pressure medium pump 38 to the one or more control valves 40. Embodiments are likewise conceivable in which the one or more pressure accumulators 43 open out into the pressure medium lines 41 which connect the one or more control valves 40 to the actuating devices 10 a,b.

In addition to the use of the pressure accumulator 43 in applications for variably adjusting the control times of an internal combustion engine 1, the pressure accumulator 43 may also be used in other vehicle applications, for example in switchable cam followers or in applications in automatic transmissions.

LIST OF REFERENCE SYMBOLS

1 Internal combustion engine

2 Crankshaft

3 Piston

4 Cylinder

5 Traction mechanism drive

6 Inlet camshaft

7 Outlet camshaft

8 Cam

9 a Inlet gas exchange valve

9 b Outlet gas exchange valve

10 Device

10 a First actuating device

10 b,c Further actuating device

21 Sprocket

22 Outer rotor

22 a Housing

23 Inner rotor

24 Side cover

25 Side cover

26 Hub element

27 Vane

27 a Vane springs

28 Vane grooves

29 Circumferential wall

30 Projection

32 Fastening element

33 Cavity

34 Delimiting wall

34 a Early stop

34 b Late stop

35 First pressure chamber

36 Second pressure chamber

37 Pressure medium supply device

38 Pressure medium pump

39 Tank

40 Control valve

41 Pressure medium line

42 a Check valve

42 b Check valve

42 c Check valve

42 d Check valve

42 e Double check valve

43 Pressure accumulator

44 Pressure reservoir

45 Pressure piston

46 Spring element

46 a Vent

47 First pressure surface

48 Second pressure surface

49 Store chamber

50 Control chamber

51 Store line

52 Control line

53 First directional valve

54 Stop

55 Connecting line

56 Directional valve

57 Second directional valve

58 Counterpressure chamber

59 Third pressure surface

60 Control means

A First working port

B Second working port

P Inlet port

T Discharge port

P₁ Pressure port

T₁ Discharge port

A₁ Control chamber port

B₁ Store chamber port

V₁ Store port

G Counterpressure port 

1. A device for variably adjusting control times of gas exchange valves of an internal combustion engine comprising: a drive input element; a drive output element; at least one pressure chamber; a pressure medium supply device; and at least one pressure accumulator, with it being possible for pressure medium to be supplied to or discharged from the at least one pressure chamber by means of the pressure medium supply device, with it being possible for a phase position of the drive output element relative to the drive input element to be varied by means of the supply of pressure medium to or discharge of pressure medium out of the pressure chamber, with the pressure accumulator having a movable element which is provided with a first pressure surface which partially delimits a store chamber, with the store chamber being connected to the pressure medium supply device, with it being possible by means of the pressurization of the store chamber for the movable element to be moved counter to the force of a force wherein the movable element has at least one second pressure surface which partially delimits a control chamber, with it being possible by means of the pressurization of the control chamber for the movable element to be moved counter to the force of the force store, and with a pressure medium flow within the pressure accumulator from the store chamber into the control chamber being prevented,
 2. The device of claim 1, wherein, during operation of the internal combustion engine, the control chamber is selectively connectable to a pressure source or to a tank.
 3. The device of claim 1, wherein the control chamber can be emptied into a tank without diversion via a consumer.
 4. The device of claim 2, wherein control means are provided, with it being possible for the control chamber to be selectively connected to a tank or to the pressure source by the control means.
 5. The device of claim 2, wherein control means are provided, which, in a first state, block a pressure medium flow from the store chamber to the pressure medium supply device and permit a pressure medium flow to the store chamber and to the control chamber, and which, in a further state, permit the pressure medium flow from the store chamber to the pressure medium supply device and produce a connection between the control chamber and a tank without diversion via a consumer.
 6. The device of claim 5, wherein a store line is provided which connects the pressure medium supply device to the store chamber, and a control line is provided which connects the control chamber to a pressure source.
 7. The device of claim 6, wherein the control means is designed as a single directional valve which has in each case one port for the store line, the control line, the control chamber, the store chamber and the tank.
 8. The device of claim 6, wherein the control means comprise at least one first directional valve which is arranged in the control line.
 9. The device of claim 8, wherein the control means also comprise a second directional valve or a double check valve which is arranged in the store line.
 10. The device of claim 8, wherein the control means also comprise a double check valve which is arranged in the store line.
 11. The device of claim 5, wherein the store chamber and the control chamber are connected via a check valve, with a connection being arranged between control means and the store chamber and the control chamber and with the check valve blocking a pressure medium flow from the store chamber to the control chamber.
 12. The device of claim 1, wherein a check valve is provided between the control chamber and the pressure source, which check valve blocks a pressure medium flow from the control chamber in a direction of the pressure source.
 13. The device of claim 1, wherein a check valve is provided between the store chamber and the pressure medium supply device, which check valve blocks a pressure medium flow from the pressure medium supply device in a direction of the store chamber.
 14. The device of claim 1, wherein a pressurization of the store chamber moves the movable element a same direction as a pressurization of the control chamber.
 15. The device of claim 1, wherein the movable element has a third pressure surface which at least partially delimits a counterpressure chamber, with a pressurization of the counterpressure chamber moving the movable element in a opposite direction to a pressurization of the control chamber or of the store chamber.
 16. The device of claim 2, wherein a ratio between the minimum throughflow cross-section between the control chamber and the tank and the minimum throughflow cross-section between the store chamber and an actuating unit is greater than a ratio between a surface area of the second pressure surface and a surface area of the first pressure surface.
 17. The device of claim 1, wherein the store chamber and the control chamber do not communicate with one another within the pressure accumulator.
 18. The device of claim 4, wherein the control means are designed as a directional valve. 